Analysis of the causes of secondary vibration According to the phenomenon that the deflection of the first and second rotors exceeds the standard, the main cause of the secondary vibration is that the rotor is bent and the rotor dynamic balance is not good. Further analysis was made to find out the cause of the rotor bending.

As shown by the rotor structure and the locating spacer, the geometrical irregularity of the locating spacer in the figure is due to the weight loss of the original design gasket when the rotor is dynamically balanced after the impeller is assembled. Moreover, an arc groove of 28 mm in length and 6 mm in width and depth is also milled on one plane of the gasket. From the distribution of the force area of ​​the gasket, the difference between the weighted area and the unremoved side is half. According to the force (P) = pressure receiving area, the axial force distribution acting on the positioning washer when the lock nut is locked is very uneven.

The rotor structure diagram positioning spacer is shown, and the 6 end holes of the impeller are the de-weighting holes when the single impeller is dynamically balanced. The depth of the two holes in the middle is 5mm, and the depth of the four holes on both sides is 70mm. It can be seen that the distribution of the force area of ​​the end face of the impeller is uneven. From the assembly position of the positioning washer and the end surface of the impeller, the arc groove of the positioning washer corresponds to the position of the 6 holes on the end surface of the impeller, and the surface of the gasket is also pressed with two 6 and the height is 0.5 mm. Round boss.

According to the analysis, the main reason for the secondary shaft diameter bending of the first and second rotors is caused by the positioning gasket. This is because when the lock nut is tightened with a tightening torque of 900 Nm, the axial force receiving area of ​​the positioning washer is asymmetrical, the axial pressing force is unevenly distributed, and the axial force is biased, causing the rotor to be in the impeller. A bend occurs at the shaft diameter. The bending of the shaft diameter necessarily causes the rotor dynamic balance to be damaged, and the dynamic balance is not good, which inevitably causes the rotor to vibrate. Therefore, the positioning of the spacer is the root cause of the bending of the secondary impeller shaft diameter of the rotor, resulting in secondary vibration.

The reason for the wear of the secondary impeller can be seen from the structure of the rotor. The fit between the end face of the impeller and the shoulder is made by convex-concave arc-face contact. When the inspection is carried out, the contact surface has a curve with a gap and a hemp surface. This is due to the occurrence of the shaft diameter. Caused by bending. With the continuous operation of the equipment, the rotor vibration is intensified. At this time, the gas pressure difference between the impeller blades is uneven, resulting in unstable airflow and severe vibration of the rotor, resulting in friction between the impeller and the diffuser.

The secondary impeller wear aggravates the secondary vibration. Due to the uneven wear of the secondary impeller, the leakage loss in each blade is not uniform, resulting in uneven airflow vortex. This vortex gas excites the vibration of the rotor, resulting in its Not working properly.

Treatment plan formulation (1) Rotor secondary impeller shaft diameter alignment correction to eliminate deflection, so that the value is 0.01mm.

(2) The concave and convex arc surface of the rotor shoulder and the end surface of the impeller should be studied. The contact surface should be more than 80%, and should be evenly contacted.

(3) Replace the positioning pad.

(4) All the modified two-stage impeller type lines are obtained, and the impeller shape is intact, and the impeller inner hole grinding achieves the matching precision with the shaft.

(5) The secondary impeller is balanced at low speed. Before the secondary impeller is installed, the rotor is balanced at a low speed. After the secondary impeller is installed, the rotor is balanced at a low speed, and the rotor is balanced at a high speed.

Due to the difficulty in handling the defects of the rotor, the factory can't afford it. Therefore, please come to the relevant domestic professional factory for processing. Because the professional factory has different opinions on the treatment plan of the rotor and our treatment plan, the professional factory does not agree to make the blade profile correction. Therefore, the process of the rotor has gone through three stages and more than five months to complete the entire solution. Implementation.

The first stage, from December 5, 1998 to February 2, 1999, a professional factory mainly polished the secondary wheel wear burrs; the first and second rotor shoulders and the impeller end face contacted the ground; the rotor made a low speed balance . On February 2, the test was carried out, and the second, third and fourth vibrations exceeded the standard parking.

Its vibration value is more than 100m. In the second stage, on February 25, 1999, the first, second and third and fourth grade rotors were sent to a domestic compressor manufacturer. This stage is mainly for the high-speed balance of the treatment of the first and second stage rotors and the third and fourth stage rotors.

First and second stage rotor treatment (1) Two-stage impeller shaft diameter straight brush plating eliminates deflection.

(2) The secondary impeller is colored, and the flaw detection is qualified.

(3) The inner hole of the secondary impeller is ground to a standard with a cast iron rod.

(4) The wear of the secondary impeller blade profile is smooth.

(5) The secondary impeller single wheel is qualified for low speed dynamic balance.

(6) The secondary wheel rotor is not installed to pass the low speed balance.

(7) Install the secondary wheel rotor to pass the low speed balance. In order to verify whether the positioning washer is related to the bending of the shaft, the new gasket is not replaced during the first assembly. The result of the inspection is that the shaft head is bent by 0.05 mm, and the angle at which the residual unbalance value is balanced and the axial stress of the positioning gasket are weak. Consistent. Replace the new gasket to check the bending of the shaft head 0.005mm, the rotor is ideal for low-speed balance. From the comparison of the inspection data before and after the gasket replacement, the influence of the gasket on the shaft bending is very large, and it is verified that the analysis of the impeller wear is correct.

Treatment of the four-stage rotor (1) Check the radial runout values ​​of the three-stage impeller and rotor parts, which meets the technical requirements. (2) After assembly, the rotor is qualified for low and high speed dynamic balance.

From March 27th to April 17th, 1999, a comprehensive and unconventional inspection was carried out in various aspects, and 25 trials were carried out. The experts of Nangao Gear Professional Factory conducted a comprehensive inspection of the large and small gears and the Wuhan Anhuanyuan University. No problems were found in the flaw detection of the pinion.

According to the analysis of 8 rotor vibration test data of Huazhong University of Science and Technology on March 31, April 14 and 17, 1999, as shown, the following problems can be seen: the vibration of the secondary vibration side point in three starts (1) The first-order vibrational phase of the primary and secondary shaft measuring points is opposite when the working speed is reached until the protection action is stopped, and the phases of the three-stage and four-stage axial measuring points are the same.

The second-class vibration of the US 4MSGP7/15 nitrogen turbine compressor is technically successful, which is reflected in the accurate analysis of vibration causes, effective treatment measures, and satisfactory results.

The geometrical size and quality of the secondary impeller positioning gasket are unevenly transmitted when subjected to the axial tightening force of the lock nut, causing the shaft to bend and cause vibration. Poor contact between the impeller end face and the shoulder and convex arc surface can also cause vibration. The long-term vibration operation deteriorates, causing the secondary impeller to wear. The impeller wears, the blade profile breaks, the pneumatic working condition changes, the air frequency power frequency excitation occurs, and the secondary vibration is intensified, which makes it impossible to operate safely. This analysis objectively reflects the causes and development of vibration.

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